Railway well cars may be considered as upwardly opening U-shaped channels of a chosen length, simply supported on a pair of railcar trucks. Although single unit well cars are still common, there has been a trend in recent years toward articulated, multi-unit railcars which increase the number of containers per unit length of train. Further, articulated cars are cheaper to build and maintain per container slot.
Contemporary well cars may carry a number of alternative loads made up of containers in International Standards Association (ISO) sizes or domestic sizes, and of highway trailers. The ISO containers are 8'-0" wide, 8'-6" wide, and come in a 20'-0" length weighing up to 52,900 lbs., or a 40'-0" length weighing up to 67,200 lbs. Both stand-alone and articulated well cars can be all-purpose trailer on flat car ("TOFC") or container on flat car ("COFC") railcars. This means that they can carry both containers and trailers or containers only. Domestic containers are 8'-6" wide and 9'-6" high. Their standard lengths are 45', 48' and 53'. All domestic containers have a maximum weight of 67,200 lbs. Recently 28' long domestic containers have been introduced in North America. They are generally used for courier services which have lower lading densities. The 28' containers have a maximum weight of 35,000 lbs.
Two common sizes of highway trailers are, first, the 28' pup trailer weighing up to 40,000 lbs., and second, the 45' to 53' trailer weighing up to 60,000 lbs. for a two axle trailer or up to 90,000 lbs. for a three axle trailer. It is advantageous to provide well cars with TOFC and COFC hitches at both ends. This permits either a single 53' three axle trailer or, or two back-to-back 28' pup trailers to be loaded. The wheels of a trailer can rest in the well, with the front of the trailer overhanging decking at one end or the other of well car unit. A second trailer may rest in the well facing in the opposite direction. Alternatively shipping containers, typically of 20 ft., 28 ft, or 40 ft lengths, may be placed in the well, with other shipping containers stacked on top. Further, well cars may carry mixed loads of containers and trailers.
When a long highway trailer rests in the well of one unit of a multiple unit articulated well car, the nose of the trailer is held in a king pin mount on the end structure of that same unit, and can overhang both the articulated connection and part of the end structure of the adjacent well car unit. Larger highway trailers usually imply larger loads. A deep side beam can generally carry a greater load than a shallow beam. Deep side beams generally yield a relatively deep well. A higher load capacity also tends to require the use of a larger, 38 inch wheel truck, and a deeper end structure. The result is that the clearance from the top of the end structure of each well car unit to the underside of the nose of the highway trailer may be relatively small. For example, in the well car described herein, the design clearance is about 5.5 inches above the bolsters and running boards. The clearance above the shear plate is greater, approximately 13 inches plus a small amount. The versatility of a well car is improved if the well is designed to receive highway trailers of most common sizes. Similarly, the structure of the well car unit is generally designed not to foul a design envelope defined by the extent of the sizes of the overhanging noses of highway trailers whose wheels can be received in the well, whether in terms of height or width.
A standard AAR brake reservoir is a cylindrical steel tank approximately 16 inches in diameter and 34 inches long. The reservoir has an internal curved plate which divides the cylinder into two compartments. One compartment is an auxiliary compartment for containing compressed air used for service brake applications. The other compartment is an emergency compartment, also for containing compressed air, and is used in emergency brake applications when more rapid braking is required. Both the brake valve and the brake reservoir are too large to fit within the 5.5 inch height restriction of the well car described herein, beneath the nose of the overhanging trailers.
A compressed air trainline is formed when the cars of the train are coupled together. Compressed air from the locomotives is supplied through the trainline to charge the various reservoirs. The normal charge in the reservoirs is 90 p.s.i.g. When the locomotive engineer applies the brakes under normal service conditions, pressure is bled down from the train line, to 85, 80 or 75 p.s.i.g., for example. This causes the brake valve in each successive car to bleed pressure from the auxiliary reservoir to the car's brake cylinder or cylinders to match the lowered pressure in the trainline. The air bled from each auxiliary reservoir is bled to its respective brake cylinder, and causes the brakes to be applied, either gently or more firmly depending on the pressure level selected by the locomotive engineer. In normal operation it takes a significant length of time for the signal of the pressure drop in the train line to reach the last car in the train, and for the pressure to stabilize at the particular value selected by the train locomotive engineer.
The brake valve will only open the emergency reservoir when the pressure drop in the trainline is large and rapid. It is desirable that an emergency signal travel down the trainline more quickly than in normal operation. When emergency operation is selected to "dump" the trainline, the brake valve not only causes both the auxiliary and emergency reservoirs to be opened to the brake cylinders, but also causes a valve to vent the trainline to ambient at that specific car, rather than having to drain all the way back to the locomotive. The rapidity of the emergency brake response is then a function of the distance between the valves that vent, or "dump", the trainline to ambient. The American Association of Railroads (AAR) standard S-401-92 requires that the length of brake pipe between any two adjacent control valves not exceed 175 feet, to give desired emergency brake performance. A more equal spacing of the brake valves leads to a more even time lapse between successive brake valve actualizations and hence a more uniform brake application from one car to the next. The term "uniform" means that there is less time delay in the brake application from one car to the next. This in turn results in less slack action in the train.
Traditionally, brake valves and brake reservoirs have been located on top of the end structure of the articulated well car units. The need to maintain clearance from the noses of the highway trailers, as noted above, requires a different placement. One alternative is to locate the brake valve in the space between the car units, above an articulation truck. However, the space available tends to be limited by the requirement that the cars be able to follow a 180' bend radius.
In light of the foregoing, there is a need for a multiple unit articulated railcar that can satisfy the twin requirements that the brake valves and brake reservoirs not interfere with overhanging highway trailers that can fit in the very restrictive space between adjacent intermediate units and that they not be separated by more than 175 feet.
The U-shaped section of the car is generally made up of a pair of spaced apart left and right hand side beams, and structure between the side beams to hold up whatever load is placed in the well, and to carry shear between the beams under lateral loading conditions.
In earlier types of well car the side beams tended to be made in the form of a single, large beam. While simple in concept, they were often wasteful, having a large weight of material in locations where stress may have been low. It is advantageous to design a sill in the form of a hollow section, of relatively thin walls, and to provide local reinforcement where required. It is also advantageous that the hollow section be formed at the mill as a hollow tube or roll-formed section where possible, rather than welded. This often yields a saving in effort, may permit the use of a higher yield stress steel, and may also reduce the number of stress concentrations in the resulting structure. As the wall thickness decreases the prospect of buckling under buff loads increases, and measures to increase stiffness and hence to increase the buckling load would be advantageous. It would also be advantageous to provide protection for the sills to discourage damage to the sills due to clumsy loading of trailers or containers.
In the past one method of dealing with areas of higher flange stresses in the side construction stress concentration was to use a member of greater weight. As the thickness of structural members is reduced it would be advantageous to transfer loads from the railcar trucks to the bolsters, and thence to the side sills, more smoothly to discourage or reduce stress concentrations. One way to do this is to increase the depth of section at the bolster, with a consequent increase in height of the end decking.